The optimization of the design or configuration of several critical mechanical components in a gas turbine engine cannot presently be realized with conventional analysis techniques. Conventional optimization and design techniques fail because computational fluid dynamic models for systems such as a gas turbine engine are not sufficiently validated to insure accuracy. For example, it would be highly desirable to optimize the design of gas turbine compressor blades. Valid results must be based upon accurate fluid dynamic modeling of the pressure, temperature and flow rates of gasses within the compressor environment. The development of suitably accurate models would require the measurement of pressure with two-dimensional spatial resolution and high temporal resolution. Such measurements are not currently possible.
In general, the measurements of gas pressure and flow over time may be made with selected spectroscopic techniques, for example tunable diode laser absorption spectroscopy (TDLAS). For example, the TDLAS measurement of selected combustion parameters is described in U.S. Pat. No. 7,248,755 titled; Method and Apparatus for the Monitoring and Control of Combustion, which patent disclosure is incorporated herein by reference for all matters disclosed therein. The primary difficulty in making TDLAS measurements in a gas turbine compressor or other highly variable environment involving rapidly moving mechanical components is a lack of sufficient signal to noise available in the short time duration available to average the acquired spectra while still maintaining adequate temporal resolution. For example, distributed feedback (DFB) diode lasers can be tuned over a spectral range of a few tenths of a nanometer at up to a few 10's of kilohertz which allows measurements to be made at perhaps a 1 kHz update rate given the averaging required to produce good SNR in the turbulent environment of a gas turbine engine. Such an update rate can be adequate for path averaged measurements in the hot section of the engine. However, in order to map the temperature or pressure field in the compressor zone and to provide adequate temporal resolution to “freeze” the motion of the compressor blades relative to the stators requires a different measurement method with enhanced temporal resolution characteristics.
A brief calculation will serve to illustrate the challenges presented by any attempt to use standard wavelength-scanned methods of making TDLAS measurements to measure pressure in the compressor environment with high temporal resolution. Compressor blade assemblies typically rotate at approximately 10,000 rpm.10000 rpm=167 revolutions/secondA compressor assembly might consist of approximately 60 compressor blades for a low pressure compressor, which means that compressor blades pass by a particular stator at a frequency of 10 kHz. Given that it is only possible to scan a laser across the necessary absorption frequencies a few times faster than this rate; and in view of the requirement to average many scans to produce a spectrum with sufficient SNR for analysis, conventional TDLAS strategies lack the necessary temporal resolution to “freeze” the motion of the compressor blades and see the temporal pressure transients that must be observed and studied. The embodiments disclosed herein are directed toward overcoming one or more of the problems discussed above.